Half precision floating point

Standardizing Bodies

• Format
  • IEEE
  • ISO/IEC/IEEE JTC 1/SC 25
• C
  • ISO/IEC JTC 1/SC 22 WG 14 (C WG)
    • http://www.open-std.org/JTC1/SC22/WG14/
• C++
  • ISO/IEC JTC 1/SC 22 WG 21 (C++ WG
    • http://www.open-std.org/JTC1/SC22/WG21/
• Fortran
  • ISO/IEC JTC 1/SC 22 WG 5 (FORTRAN WG)
    • https://wg5-fortran.org/
• MPI
  • MPI Forum
    • http://mpi-forum.org/

Standardizations

Format

• IEEE 754-2008 - IEEE Standard for Floating-Point Arithmetic (2008-08-29)
  • http://ieeexplore.ieee.org/servlet/opac?punumber=4610933
  • binary16 is defined as a format
• ISO/IEC/IEEE 60559:2011
  • http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=57469
  • Same as IEEE 754-2008

C

• ISO/IEC JTC 1/SC 22/WG 14 N1945 (ISO/IEC TS 18661-3:2015): Information technology - Programming languages, their environments, and system software interfaces - Floating-point extensions for C -

  • http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=65615 (2015-10)
  • http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1945.pdf (2015-06-10)
  • ISO/IEC TS (technical specification) which adds IEEE 754-2008 support to C
  • _Float16 and _Float16 _Complex are defined as types for IEEE 754-2008 binary16
  • Extension of ISO/IEC 9899:2011
  • Not included in ISO/IEC 9899:2017 (C18)

• ISO/IEC JTC 1/SC 22/WG 14 N2016: Adding Fundamental Type for Short Float

  • http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2016.pdf (2016-02-14)
  • Same as ISO/IEC JTC 1/SC 22/WG 21 P0192R1 of C++

C++

• C++ Standards Committee Papers

  • http://www.open-std.org/jtc1/sc22/wg21/docs/papers/

• ISO/IEC JTC 1/SC 22/WG 21 P0192R0: Adding Fundamental Type for Short Float

  • http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0192r0.pdf (2015-11-11)
  • short float is proposed for C and C++ as new float type, shorter than 32 bit
  • No description about complex types

• ISO/IEC JTC 1/SC 22/WG 21 P0192R1: Adding Fundamental Type for Short Float

  • http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0192r1.pdf (2016-02-14)
  • Improved version of P0192R0
  • Same as ISO/IEC JTC 1/SC 22/WG 14 N2016 of C

• ISO/IEC JTC 1/SC 22/WG 21 P0303R0: Extensions to C++ for Short Float Type

  • http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0303r0.pdf (2017-10-15)
  • Based on P0192R1
  • Modification points against current C++ working draft are shown
  • std::complex<short float> is added for a C++ complex type

• ISO/IEC JTC 1/SC 22/WG 21 P0192R4: short float and fixed-size floating point types

  • http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0192r4.html (2018-10-08)
  • Improved version of P0192R1
  • short float
    • Same as or shorter than float
    • Bit length is not specified
  • std::complex<short float>
  • std::float16_t, std::float32_t, std::float64_t
    • IEEE 754-2008 -compliant types
    • Bit length is specified

MPI

• 16-bit floating-point support for C/C++
  • https://github.com/mpi-forum/mpi-issues/issues/65
• define language-agnostic, IEEE types|
  • https://github.com/mpi-forum/mpi-issues/issues/66
• Data type naming rule
  • https://github.com/mpi-forum/mpi-issues/issues/74
• pt2pt wg FP16 MPI Forum Meeting Dec 4 - Dec 7, 2017, San Jose
  • https://github.com/mpi-forum/mpi-forum.github.io/blob/master/slides/2017/12/FP16-201712-AH-rev4.pdf
• MPI Forum virtual meeting FP16 Jan 31, 2018
  • https://github.com/mpi-forum/mpi-issues/files/1672779/FP16-20180131-AH-rev1.pdf

Emulators

QEMU

• AArch64 v8.2 FP16 extensions is supported for ARM starting from QEMU 2.12
  • https://wiki.qemu.org/ChangeLog/2.12#ARM

Compilers

GCC

• _Float16 and __fp16 are supported in C and C++ for ARM starting from GCC 7
  • https://gcc.gnu.org/onlinedocs/gcc/Floating-Types.html (latest version)
  • https://gcc.gnu.org/onlinedocs/gcc/Half-Precision.html (latest version)
  • https://gcc.gnu.org/onlinedocs/gcc-7.1.0/gcc/Floating-Types.html (GCC 7.1.0)
  • https://gcc.gnu.org/onlinedocs/gcc-7.1.0/gcc/Half-Precision.html (GCC 7.1.0)

LLVM

• _Float16 and __fp16 are supported in C and C++ for all(?) platforms starting from clang 6
  • https://clang.llvm.org/docs/LanguageExtensions.html (latest version)
  • http://releases.llvm.org/6.0.0/tools/clang/docs/LanguageExtensions.html#half-precision-floating-point (clang 6.0.0)

MPI Libraries

Open MPI

• GtiHub issue of MPI_REAL4 and MPI_COMPLEX4

  • https://github.com/open-mpi/ompi/issues/2653

• Prototype implemenataion of MPI_SHORT_FLOAT, MPI_C_SHORT_FLOAT_COMPLEX, and MPI_CXX_SHORT_FLOAT_COMPLEX

  • https://github.com/kawashima-fj/ompi/tree/pr/fp16

MPICH

• GitHub issue and PR for MPIX_C_FLOAT16
  • https://github.com/pmodels/mpich/issues/3389
  • https://github.com/pmodels/mpich/pull/3401